1. Field of the Invention
The present invention relates to a digital watermarking apparatus which embeds information relating to copyright protection in data such as video data or audio data, and an application apparatus using the digital watermarking apparatus.
2. Related Art
Recently, a digital versatile disc (DVD) has been remarkably wide-spread and a reproducing apparatus using the DVD has been introduced to an airplane or a museum.
Especially, for application in the airplane, since a film is sometimes shown before release in theaters, there is a strong demand for a system implementing the copyright protection such that contents such as the film before release will not leak out or even if it leaked, the source of the leaked contents can be tracked.
Conventionally, as a method of the copyright protection, there is a technique called “digital watermark” which embeds specific information in the contents such as video or audio (see Japanese Patent No. 3106985).
Information embedded as the digital watermark (referred to as “watermark information” hereinafter) include various kinds of information such as copy control information for limiting the number of copies of contents, IDs of contents, IDs of copyright owners or the like.
The watermark information mostly has an object for protecting the copyright of the contents. For example, if the copy control information is embedded in the contents, a reproducing apparatus detects the copy control information from the contents and can limit the copying operation by activating a copy preventing function. In addition, if the ID of the contents or the ID of the copyright owner are embedded, even if an illegal copy is made, the watermark information is detected from the contents and the copyright owner is certified according to detected numeral values or symbols, whereby the copyright of the contents can be claimed.
Thus, since the watermark information is for protecting the copyright of the contents, it is important that there is no error in the watermark information itself, that is, there is no error in numeral values and symbols to be embedded as the watermark information.
Furthermore, in order to correctly detect the watermark information from the contents, it is important that the apparatus for embedding the watermark information correctly embeds the watermark information in the contents according to a specific correct operating method or processing procedure.
As a technique for preventing the alteration of the watermark information embedded in the contents, there is a method in which the watermark information is encrypted and then embedded in the contents (see Japanese Patent Laid-Open Publication No. 2001-78013, and Japanese Patent Laid-Open Publication No. 2002-232412).
Once the watermark information is embedded in the contents, it is difficult to alter or remove it. However, it is relatively easy to alter the watermark information before it is embedded in the contents. In other words, according to the conventional digital watermarking apparatus, there is a problem in that the watermark information itself can be altered at a stage before the watermark information is embedded in the contents.
If the altered information is embedded in the contents, for example, the copy control information of the contents becomes numeral values or symbols which show that copying is possible at any number of times or the ID of the contents or the ID of the copyright owner becomes different from its original numeral values or the symbols so that the copyright owner cannot be certified, or the like. As a result, the right of the copyright owner is considerably damaged.
In addition, the digital watermarking apparatus often uses set values necessary for the embedding operation such as a mode designation value of the embedding operation, various kinds of constant values or variables used in the embedding operation, a comparative value, a table value, sign data or the like during the watermark embedding operation. It is not until these set values are correctly set that the digital watermarking apparatus can embed the watermark information in the contents according to the predetermined correct operating method or the processing procedure.
There is a possibility that the set values necessary for the embedding operation are altered when the watermark information is embedded in the contents. If the set values necessary for the watermark embedding operation are altered, the predetermined correct operational result cannot be obtained. As a result, signal strength of the watermark information to be embedded in the contents is reduced so that the watermark information can be easily removed, or the watermark information is embedded by a method or procedure different from that assumed by the apparatus on the side for detecting the digital watermark. Consequently, the watermark information cannot be detected from the contents.